The aim of present study to analyze the occurrence and in-vitro
antimicrobial susceptibility of bacterial pathogens isolated from
surgical wound infections. Specimens from a total of 129 patients
undergoing either emergency or elective surgery were collected from
infected sites or stitch lines and inoculated onto appropriate media.
The bacterial cultures were identified utilizing standard
microbiological and biochemical methods. Isolates were tested for
susceptibility to antimicrobials using the Kirby Bauer disk diffusion
method. Statistical analysis was performed using the chi-square test. Of
129 patients investigated (62 emergency and 67 elective surgery cases),
bacterial isolates were isolated with almost equal frequency both from
emergency and elective surgery cases. Of 108 (83.72%) culture positive
samples, 62 (57.41%) were Gram negative, 39 (36.11%) Gram positive, and
7 (6.48%) showed multiple organisms. Of total 115 bacteria isolated (101
single and 7 double organisms culture positive), 33 (28.69%) were
Escherichia coli and were also the commonest; followed by Staphylococcus
aureus, 30 (26.09%) cases. S. aureus and Streptococcus spp. showed
maximum susceptibility (100%) to linezolid and vancomycin. Maximum
susceptibility of E. coli was observed to ciprofloxacin (75.7%),
followed by gentamicin (54.5%); of Klebsiella spp. to ceftriaxone and
gentamicin (66.6% each), of Proteus spp. to gentamicin (70%) followed by
ciprofloxacin (60%), and of Pseudomonas aeruginosa to piperacillin
(100%) and tobramycin (71.4%). E. coli and S. aureus were the most
common and Salmonella spp. and Acinetobacter spp. were the least common
organism causing surgical site infections. The definitive therapy
included ciprofloxacin and gentamicin for E. coli; linezolid and
vancomycin for S. aureus and Streptococcus spp; ceftriaxone and
ciprofloxacin for Klebsiella spp., Citrobacter spp., acinetobacter spp
and Salmonella spp.

Geographic Scope: India; New York Geographic Code: 9INDI India; 1U2NY New York

Accession Number:

277601640

Full Text:

INTRODUCTION

Bacterial infections at surgical sites and surgical wounds are
fairly common despite aseptic measures. Surgical site infections are
responsible for delayed wound healing, prolonged stay in hospital,
increased cost of therapy and are also important determinants of
morbidity and mortality of the patient.

Infections of surgical wounds occur whenever the combination of
number and virulence of bacteria in the wounds is sufficiently large to
overcome the local host defense mechanisms and establish progressive
growth. Essentially, all clean operative wounds contain small numbers of
bacteria at the end of the procedure, but only a small number develop
infection (1). The development of surgical site infections (SSIs) are
related to three factors firstly, the degree of microbial contamination
of the wound during surgery; secondly, the duration of the procedure,
and thirdly, host factors such as diabetes, malnutrition, obesity,
immune suppression, and a number of underlying disease states (2).
Factors leading to higher risk of infection have been described and
prophylaxis with antibiotics will definitely curtail/prevent surgical
wound infection (3,4).

Although, a large number of antimicrobial agents have been
developed more recently, yet development of resistance to large number
of antimicrobials is quite alarming. Further, imprudent use of
antimicrobial agents promotes growth of resistant micro-organisms and
can cause serious toxicity.

Initiation of optimal empirical antibiotic therapy requires
knowledge of the most likely infecting micro-organism(s) and their
susceptibilities to antimicrobial drugs (5). Thus for surgeons to decide
the appropriate prophylactic and therapeutic antibiotics, there should
be data on the spectrum of common pathogens encountered in the surgical
unit and their antimicrobial susceptibility data at each hospital
setting. The present study was therefore undertaken to explore these
relevant objectives.

METHODOLOGY

The study was carried out in 129 patients undergoing either
emergency or elective surgery in general surgery wards at Swaroop Rani
Nehru Hospital, attached to MLN Medical College, Allahabad during the
period January to December 2007. Patients of all ages and both sexes
were included in the study. The ethical committee clearance and informed
consent from patients were obtained though it was a routine sample for
diagnosis.

A personal identification number was allotted to each patient and a
detailed history, such as date of admission, date of surgery, name of
the surgical procedure relevant clinical features and associated
complaints, presence or absence of fever, presence or absence of drain,
history of antimicrobial agents used (if any) were recorded. The samples
investigated were pus, swab from the stitch line and swab from any other
infected sites, which were collected with proper aseptic precautions and
transported to the department of microbiology within two hours of
collection. For swabs an appropriate transport medium Tryticase Soya
Broth (TSB) was used. The specimen collected was divided into three
parts: first part was used to make Gram smear as per standard protocol;
second part of the sample was plated directly on the blood agar and
McConkey agar and incubated at 37[degrees]C for 1824 hours; third part
of the sample was inoculated in Brain heart infusion broth and incubated
overnight at 37[degrees]C.

This prospective study comprised of 129 patients including 62
emergency cases and 67 elective surgery cases. The majority of samples
were collected from patients who underwent abdominal surgery--104
(80.62%) cases, followed by surgery of extremities--14 (10.85%) and head
and neck 11 (8.53%) cases.

Maximum culture positive, 48/129 (37.21%) cases were in the age
group of 21-40 years, followed by 0-20 years 31 (24.03%) cases and
minimum 8 (6.20%) cases were in the age group of 61-80 years. The
chi-square test revealed insignificant ([chi square] = 4.29, DF=3,
p=0.23146525). Of 129 admitted cases, fever was present in 65 cases, and
absent in 64 cases. Among 65 febrile cases, 60 cases were culture
positive. In 64 afebrile cases 48 were culture positive. The association
between fever and culture positivity was found to be significant ([chi
square]=5.87, DF=1, p=0.0153585). Of 108 culture positive cases, 62
(57.41%) were Gram-negative, 39 (36.11%) were Gram-positive, and 7
(6.48%) cases were considered contaminated, hence these were rejected.

Out of a total 115 bacterial isolates (101 single isolate culture
positive and 7 mixed isolates (2 isolates) culture positive), E. coli
was most frequently isolated [33 (28.69%)], followed by S. aureus [30
(26.09%)]. Salmonella spp. non-typhoidal was isolated in only one case,
and that too in elective surgery case (Table 1).

It may be stated that an intermediate sensitive organism upon
judicious exposure to higher concentration of an antimicrobial agent may
become sensitive; hence intermediate sensitive organisms were considered
as sensitive to that antimicrobial agent for the purpose of the present
study. (8,9) Though opposite views have also been expressed.

S. aureus was found in 15 cases each of elective and emergency
surgery. The maximum susceptibility (100%) was observed to linezolid and
vancomycin. The maximum resistance was observed to ampicillin [22
(73.33%)], followed by trimethoprim-sulfamethoxazole, i.e., co
trimoxazole [20 (66.67%)] (Table 2). All 4 coagulase- negative
staphylococci (CoNS) isolated were susceptible to linezolid, vancomycin
and ceftriaxone. None were however sensitive to ciprofloxacin and
chloramphenicol. None of the isolates were vancomycin-intermediate S.
aureus (VISA). Streptococci were 100% susceptible to linezolid and
vancomycin. Overall maximum resistance was observed to chloramphenicol
(75%) followed by ciprofloxacin and cotrimoxazole (62.5%).

In E. coli overall maximum susceptibility was observed to
ciprofloxacin [25 (75.76%)], followed by gentamicin (54.5%). Maximum
resistance was observed to cotrimoxazole [27 (81.8%)], followed by
azithromycin (78.7%) and chloramphenicol (72.7%) (Table 3). In
Klebsiella spp. overall maximum susceptibility (66.6%) was noted with
ceftriaxone and gentamicin followed by ciprofloxacin (53.3%). Maximum
resistance was seen against cotrimoxazole (73.3%) followed by
azithromycin (66.6%) and chloramphenicol (60%) (Table 3). In Proteus
spp. maximum susceptibility (70%) was observed with gentamicin followed
by ciprofloxacin (60%). Maximum resistance was seen against azithromycin
(80%).

In Citrobacter spp. maximum susceptibility was noted with
ciprofloxacin (75%) followed by azithromycin, ceftriaxone and cefaclor
each showing 50% susceptibility. 100% resistance was noted against
co-trimoxazole. In Acinetobacter spp. 100% susceptibility was noted with
ciprofloxacin and ceftriaxone. In Salmonella spp. 100% susceptibility
was seen with chloramphenicol, ciprofloxacin, ceftriaxone and gentamicin
(Table 4).

DISCUSSION

The risk of developing surgical-site infection is dependent on a
myriad of host (intrinsic) and operative (extrinsic) risk factors (10).
Infection is an unresolved problem while undertaking any surgical
operations. Infections occur even though surgeons perform thoroughly
clean procedures during surgery and patients are strictly managed before
and after surgery. Despite the availability of a large arsenal of
antimicrobial agents the ability of bacteria to become resistant to
antibacterial agents is amazing. This is more evident in hospital
settings where antimicrobial agents are being used profusely. A changing
pattern of isolated organisms and their antimicrobial sensitivity; (it
varies from hospital to hospital and region to region) is a usual
feature. Many a time patients' lives are lost after extensive
surgery, owing to microbial infections and improper treatment. Thus, the
study is clinically relevant in the present scenario by not only
observing the spectrum of microorganisms isolated from surgical patients
(nosocomial infections) but also in evaluating their antimicrobial
susceptibility pattern.

In this prospective study, samples were collected from 129 patients
admitted in the surgery wards. Of 62 cases of emergency surgery 54
(87.09%) were culture positive, and of 67 cases of elective surgery, 54
(80.59%) were culture positive. These observations depicted that a high
infection rate (83.72%) was prevailing currently in these setting in
this region of the state and that the infection rate was comparable in
both the groups, unlike other previous studies where infection in the
emergency surgery was significantly higher as compared to elective
surgery. This calls for more stringent steps for proper disinfection and
sterilization during the elective surgery cases. Moreover, infection
leads to protracted hospitalization, patients risk complications
associated with additional surgery and antimicrobial treatment as well
the possibility of renewed disability. (11)

The predominance of males 71 (65.74%) in culture positive cases is
probably due to more exposure to the environment and more chances of
accidents while earning livelihood. A higher involvement of males has
also been reported by other workers in the field. There was
statistically no significant difference in male to female infection
rate.

The age distribution of cases ranged between 0-80 years with
younger and most productive, 21-40 years age group being maximally
involved [48 (37.21%)]. The involvement of younger age group was quite
significant. Moreover, the infection rate was also maximal in the age
group of 21-40 years and least in 61 to 80 years age group.

An attempt was also made to correlate the presence of fever with
culture positivity. Out of 65 febrile cases, positive culture was found
in 60 cases (92.30%). Whereas out of 64 afebrile cases, positive culture
was found in only 48 cases (75%). This observation was in conformity
with general concept that infection is associated with fever. The
explanation is infection causes release of pyrogens, which elevate the
body temperature. (12)

There was predominance of Gram-negative organisms over Gram-
positive organisms. A higher rate of infection due to Gram-negative
organisms, [62 (57.41%)] in this study is because the study comprised of
nosocomial infections and majority of specimens were collected from
abdominal surgery cases. As abdominal surgeries usually involve organ
perforation, gut surgeries and handling of gut, that may cause spillage
of gut flora which of course is rich in Gram-negative organisms, hence a
greater infection rate with Gram-negative organisms. The facultative
organisms most commonly isolated from intraabdominal infection are
Escherichia coli and Enterococcus faecalis. (13,14) Ananthnarayan et al
(15) reported that enteric Gram-negative bacilli were the most common
hospital pathogens. Zaleznik (16) also found that Gram-negative bacteria
were the commonest cause of nosocomial infections.

According to Keshari et al (17), of 92 isolates, 54 were
Gram-negative bacilli and 38 Gram-positive cocci and Klebsiella spp. and
E. coli were more common in a study carried out in septicemic neonates.
Khosravi et al (18), in a study on post-operative infections of
orthopedic bone implants observed S. aureus [34 (21.94%)], Klebsiella
ozaenae [26 (16.77%)] and P. aeruginosa [24 (15.50%)] being the most
common causative agents in variance to our observations. Further, while
investigating the antimicrobial susceptibility of bacterial isolates
from tracheal specimens obtained from pediatric patients from Tehran,
Jafari et al (19) observed Pseudomonas spp. to be the most prevalent
bacterial isolate (32%) followed by S. aureus (27.6%), Klebsiella spp.
(16%) and Enterobacter spp. (9.6%).

In the present study, among the total 115 bacterial isolates there
were 101 single isolate culture positive and 7 (6.08%) double isolate
culture positive. Khosravi et al (18) also reported that among the
positive cultures less than 2% were mixed bacterial culture of two
organisms. Regarding the distribution of bacterial isolates in the
samples, it was observed that E. coli and S. aureus were the commonest
organisms both in emergency and in elective surgery cases. Salmonella
(non-typhoidal) was grown in only one case. Mixed infections were noted
in 7 (6.48%) cases and most of them were from burn patients. Our
findings are in conformity with those of Sanyal et al. (20) As most of
the samples were from abdominal surgery; hence in these cases more Gram
negative bacteria were isolated. Most of the P. aeruginosa isolates were
from burn patients. Madoff (21) reported that P. aeruginosa as one of
the commonest bacteria causing infection in burn patients. Ganesamoni et
al (22) also found P. aeruginosa being the commonest (81.1%) and
responsible for serious infection in burns.

Our findings in respect to susceptibility pattern of S. aureus in
emergency and elective surgery cases showed that maximum susceptibility
(100%) was noted to linezolid and vancomycin. Our findings are in
conformity with those of Shobha et al (23) who found all isolates of S.
aureus were sensitive to vancomycin. Archer and Polk (24) reported that
vancomycin is the drug of choice for methicillin resistant S. aureus
(MRSA). Linezolid is an FDA approved agent for the treatment of
infections caused by methicillin susceptible and resistant strains of S.
aureus. (25) Thus our findings are in agreement with these authors. As
far as the susceptibility pattern of CoNS was concerned maximum
susceptibility was observed with linezolid and vancomycin in 100% cases.

Since the emergence of methicillin-resistant Staphylococcus aureus
(MRSA), glycopeptides like vancomycin are frequently being used as agent
of choice for the treatment of infection caused by MRSA. Although, the
incidence of vancomycin-intermediate S. aureus (VISA) and
vancomycin-resistant S. aureus (VRSA) has been rising in various parts
of the world yet documented reports of VISA/VRSA in India are few. It
may be mentioned that in the present study vancomycin-intermediate S.
aureus (VISA) were not found. Menezes et al (26) in their study from a
tertiary care hospital of southern India reported that out of a total of
261 Staphylococcal isolates (141 S. aureus isolates and 120 coagulase
negative Staphylococci), there were 6 VISA strains (1 from S. aureus
isolate and 5 from coagulase-negative Staphylococci). Kapil (27) also
reported presence of VISA in their study. Moreover, Tiwari et al (28) in
their study from northern part of India reported the presence of both
vancomycin-resistant Staphylococcus aureus (VRSA) and
vancomycin-intermediate (VISA) as well as teicoplanin-intermediate. The
authors studied a total of 1681 Staphylococcal isolates consisting of
783 S. aureus and 898 coagulase-negative Staphylococci (CoNS). Authors
reported that out of 783 S. aureus, two S. aureus strains were found to
be vancomycin and teicoplanin resistant and 6 strains of
vancomycin-intermediate. One CoNS strain was resistant to vancomycin and
teicoplanin and two CoNS strains were intermediate to vancomycin and
teicoplanin. Moreover, two VRSA strains were also found to be resistant
to several other antimicrobials such as gentamicin, tobramicin,
amikacin, norfloxacin, ciprofloxacin, erythromycin, tetracycline,
cotrimoxazole, and cefaperazone/sulbactam.

Our findings in respect to susceptibility pattern of Streptococcus
spp. showed that maximum susceptibility was noticed with Iinezolid and
vancomycin in 100% cases. Linezolid is approved by FDA for the treatment
of infections caused by Streptococcus spp. They are highly susceptible
to vancomycin as well. (25)

Regarding the susceptibility pattern of E. coli it was observed
that maximum susceptibility was noted with ciprofloxacin in 75.76% cases
followed by gentamicin 54.54%. Fluoroquinolones are potent bactericidal
agents against E. coli and ceftriaxone has also been found to be a
useful drug for the treatment of infections caused by
Enterobacteriaceae. (29) Regarding the susceptibility pattern of
Klebsiella spp. it was noted that maximum susceptibility was with
ceftriaxone in 66.67% cases. In short, antimicrobial susceptibility test
revealed a high rate of antimicrobial resistance to the most antibiotics
used in this study suggesting a horizontal spreading of resistance among
the isolates. It is found that most of the organisms were susceptible to
vancomycin, linezolid and ciprofloxacin. Khosravi et al (18) reported
that the staphylococci which was the major isolate, showed high
sensitivity to vancomycin in conformity with our observations. It may be
emphasized that the consequences of increased drug resistance are
far-reaching. Bassetti et al (30) has observed that accurate information
on local epidemiology and antimicrobial resistance pattern of pathogens
is essential to select clinically effective antibiotic therapy for
infection.

In conclusion, it is observed that both rate of infection and
bacterial resistance to commoner antimicrobial agents are fairly high in
our study thus necessitating treatment with the second or third
generation antimicrobial agents, hence escalating the cost of treatment
with remarkable economic impact, and increasing hospital stay. Moreover,
increased bacterial resistance is probably due to irrational and
inappropriate use of antimicrobial agents, disregard to hospital
infection control policies and showing negligible regard to culture
susceptibility pattern while administering antimicrobial agents. The
study provides important feedback data to choose empirical therapy in
cases of surgery based on the knowledge of commonly isolated organisms
and their antimicrobial susceptibility pattern.